any organic substance that occurs in neural activity

a catecholamine secreted by the adrenal medulla in response to stress (trade name Adrenalin); stimulates autonomic nerve action

an amino acid that is found in the central nervous system; acts as an inhibitory neurotransmitter

a neurotransmitter that is a derivative of choline; released at the ends of nerve fibers in the somatic and parasympathetic nervous systems

a 36-amino acid neuropeptide that acts as a neurotransmitter in the brain and in the autonomic nervous system of humans; slight variations of the peptide are found in many other animals.

a common natural compound synthesized by decarboxylation of the amino acid arginine.